Baby getting used to formula? Help

Lea

I have been supplementing recently. I still breastfeed my baby at night. But during the day I’ve been giving him Gerber Soothe. And honestly I loved it the first week, it helped get rid of his thrush and his gas. However we’re going on a week and a half and the past few nights he has been screaming his head off because he’s trying to go poop. He went poop the night before last, but he did not go last night. Is this just his digestive system getting used to this type of formula? Or is it constipation. When he does poop it isn’t super hard and it’s pasty like it’s supposed to be but he is just so uncomfortable every night from trying to poop.